1. Field of the Invention
This invention relates to a homeostatic organ preservation system, and more particularly relates to a method and apparatus for perfusing an organ or the whole body of a non-heart beating cadaver. Even more specifically, the invention relates to a pump for use in an organ preservation system.
The science of organ preservation has been rapidly increasing in importance over recent years because of the increase in organ transplantation as a medical procedure. Basically, in organ preservation, an organ, such as a kidney, pancreas, liver, lung or heart, is removed from a donor and maintained in a viable condition by artificial means. This is done to maintain the organ until the recipient is selected and prepared to receive it.
Current procurement technology allows the removal of organs from brain-dead trauma victims, that is, heart-beating donors who are otherwise in good physiological state. Another source of transplantable organs is victims of motor vehicle accidents who succumb to their injuries in the emergency room or in the intensive care unit, in other words, non-heart beating donors. However, utilization of organs removed from these donor sources is limited, basically because of the time required to obtain consent from the families of the potential donors prior to retrieval of such organs and the need to secure an operating room. Accordingly, in situ flush and cooling of organs would be advantageous in such situations.
Irrespective of the source from which the donor organs are retrieved, it is important to cool the targeted organ rapidly to minimize the deleterious effects of warm ischemia to the organ's microvasculature. Usually, a rapid flush of the organ's microvasculature, which results in the rapid cooling of the organ, for example, to less than 15.degree. C. in the case of a kidney, and removal of red blood cells from the microcirculation should be performed as soon as possible, for example, within about one half-hour in the case of a kidney, following cessation of blood flow through the organ. This rapid cooling of the organ should be followed by the maintenance of cold temperature for a given period of time while the recipient is selected and prepared to receive the organ.
2. Description of the Prior Art
Generally, current organ preservation systems incorporate a pump which is designed to deliver cold perfusate at a constant flow. During perfusion, as the organ's vascular resistance increases, the perfusion pressure increases to maintain flow. Accordingly, one of the problems with current organ preservation pumps is that they tend to damage the delicate microvasculature of the organ which, in turn, causes the microvasculature resistance to further increase. In response to this further increase in resistance, the conventional pump further increases pressure, resulting in greater tissue injury.
A typical organ preservation pump is Model No. MOX-100TMA, manufactured by Waters Instruments, Inc. of Rochester, Minn. The Waters Instruments pump, in many ways, simulates the action of the heart in providing a cold perfusion solution to a donor organ previously removed and being maintained in a viable state prior to transplantation. The pump incorporates a lever arm which compresses an elongated resilient tube. The tube is coupled to the donor organ. The frequency of compression of the lever arm is manually adjustable, but usually is set at a relatively high pulse rate, that is, about 60 beats per minute. This action causes perfusate to flow into the donor organ. In the above described Waters Instruments Company device, the donor organ is maintained in a container connected to the machine. It is the perfusion solution which cools the organ. Thus, if perfusion ceases, the organ will warm up and damage to the organ may occur.
There are also non-pulsating types of organ perfusion apparatuses. Such apparatuses provide a preset "trickle" flow of perfusate to the isolated organ. Generally, these devices do not have any feedback control of the perfusate flow rate or pressure. Without such feedback control, there is no way of determining whether the organ is being sufficiently perfused. A hypothermic isolated organ does not have the neurological connection to protect itself by constricting its vasculature under high pressure conditions, or by dilating to open its capillaries to allow more flow. Thus, without feedback control, these apparatuses may be providing perfusate to the organ at inadequate or undesirably high volumes and pressures.
Besides the problem of forcing a given volume of perfusion solution into the organ under excessive pressure, which may result in damage to the organ's microvasculature, conventional organ preservation systems generally do not allow for the low pulse rates required during hypothermic organ perfusion. Furthermore, current machines are limited to a few hours of battery power and need frequent replacement of the ice container.
In addition, currently available organ preservation machines can weigh more than 25 kilograms and are relatively large. Such machines also may cost upwardly of $15,000 or more and $500 per disposable cassette, if such is provided.